Beta Sheet

So now that we know about the beta strained, we can talk about beta sheets so beta sheets just consist of two or mawr beta strands arranged side by side, and beta sheets are also known as beta pleated sheets. And if you Google pleaded, anything pleaded, cups, pleated pants, pleated shorts, whatever pleaded, just mean zigzag. And if we take a quick look at our example down below of our beta sheets over here, what you'll see is that we've got this zigzag type of structure to the beta sheets noticed that the are groups which are in yellow. Here. The are groups which are in yellow, uh, these yellow balls, they go down, then up, down, then up, down, then up. And they create this zigzag type of structure. And that's really what the pleated sheets are referring to the pleated is referring to. And so these are groups that go down, up and down, up and down there, actually perpendicular to the beta sheets themselves. So they're perpendicular to the plane of the beta sheets. So notice they're they're going straight up and straight down, up, above and down below the beta sheet plane, whereas the hydrogen bonds. Remember they're perpendicular, but they're perpendicular to the directions of the beta strands. And so, if we were to consider the directions, remember that the beta strands can be portrayed as arrows, and the arrows always point towards the C terminal end. And so this were a narrow here. It would be pointing this direction like this. This one would be pointing in the opposite direction. This one would be pointing this way, and then this one would be pointing this way like that. And so what you can see is that the hydrogen bonds, which are in red here, that they are going, uh, perpendicular to the directions of these beta strands. So it's something important to keep in mind. So, unlike Alfa, Healy sees something that's also important to keep in mind is that the hydrogen bonds in the beta sheets can actually form between either separate protein chains, which would mean they are inter chain hydrogen bonds or they could form between the same chain. And that would mean that they are interchange hydrogen bonds and we'll be able to distinguish that in our example down below Now, typically, beta sheets have Onley between two and five beta strands, but it's possible for them to have up to as many as 10 or even Mawr beta strands arranged side by side. So let's take a look at our example where we can distinguish between inter and intra chain pleaded sheets, beta pleated sheets. So again, over here on our left side, beta sheets are also known as beta pleated sheets. And that's because of their zigzag structure, which is seen here with er groups again that go down and up, down and up, down and up. So that's what it means by the pleaded part. Now, over here in this image, which will notice, is that the two beta strands that are being shown here with these arrows. So this arrow here and this arrow over here, uh, noticed that they are not connected. So this one curves this way and the other one curves this way. And these two are, uh, separate poly peptide chains. These chains are not connected. And so because these are separate protein chains, what this means is that this is an inter. This is an inter chain, so an inter chain beta sheet and so interchange beta sheets just means that the hydrogen bonds that form between the beta strands are on opposite poly peptide chains. And so we've got this poly peptide chain up here and this one down below. And the hydrogen bonds again are here, uh, in these dotted black lines that formed between the separate poly peptide chains. Now, over here, what you'll notice is that we've got one continuous poly peptide chain that has three beta strand. So here's one beta strand, and then it's connected. So this is a continuous one poly peptide chain. Here's our second beta strand, and then it's connected. And then here's our third beta strand. And so these beta strands, because they're all part of the same poly peptide chain, this is an intra chain beta sheet intra chain, and so interchange just means that it's all part of a single one poly peptide chain. And, uh, this is something that's incredibly different than Alfa Hillis is because Alfa Healy sees cannot form interchange hydrogen bonds, and that's where you have separate poly peptide chains. So because beta sheets conform both interchange beta sheets and intra chain beta sheets that makes them uniquely different than the Alfa, he'll seize which can Onley form intra chain hydrogen bonds. So that concludes this lesson here on beta sheets. We'll get a little bit of practice, and then we'll talk about beta sheet bond angles and a Rama Condron plot, so I'll see you guys in that practice video.

So, as you guys already know, beta sheets require a very particular set of fi and side bond angles. And it turns out that when you plot these beta sheet fi inside bond angles on a Rama Condron plot that they actually fall into the upper left quadrant of the Rama Condron plot. And so if we take a look at our example down below, which will see is that we've got this Ramachandran plot on the left over here and notice that it's broken up into these quadrants and again on the X axis, we have the five bond angles and on the Y axis on the side of the Ramachandran plot, we have the Cy Angles. And so again, the beta sheet find side bond angles and the beta strand find side bond angles fall into the upper left quadrant right up here. And so again, because the beta strands fall into the upper left, that means that the beta sheets also fall into the upper left quadrant. So taking a look at this Ramachandran plot over here again if we break it up into quadrants, which will see, is that the beta sheets again are falling into the upper left quadrant, and so notice that we have actually two different types of beta sheets that we need to distinguish between. And those are anti parallel beta sheets and parallel beta sheets, and notice that they have slightly different locations that they fall in within this upper left hand quadrant. So if you analyze a Rama Condron plot close enough, you can actually distinguish between these different types of beta sheets. And again, you can also distinguish between all types of secondary structures. And so we'll talk a lot more about the differences between anti parallel beta sheets and parallel beta sheets in our next couple of videos. So before we get there, we're actually going to get some practice with beta sheet bond angles, so I'll see you guys in that practice video.